1. Field of the Invention
The present invention is directed to multilayer containers of aromatic polycarbonate layers and particular amorphous polyamide layers, and more particularly to multilayer containers having improved stress craze and crack resistance and improved rewashing properties at elevated temperatures by utilizing particular amorphous polyamide layers in combination with polycarbonate layers.
2. Description of Related Art
Multilayer containers are well known in the prior art containing layers of polycarbonate and amorphous polyamides. Such prior art includes U.S. Pat. No. 4,513,037 to Collins which discloses polycarbonate and gas barrier layer containers having good barrier properties and good impact strength. Specifically, the reference discloses an outer layer of a polycarbonate, an intermediate gas barrier layer of either a polyester or an acrylonitrile or polymers of ethylene and vinyl acetate, and an inner layer of a polycarbonate.
Another U.S. Pat. No. 4,937,130 to Clagett et al discloses multilayer containers of an aromatic polycarbonate outer layer, an amorphous intermediate layer and an inner layer of a polycarbonate. The container of the patent is said to have excellent barrier properties and hot fill capabilities. Specifically, the reference discloses that adjacent to the intermediate layer is at least one layer of a blend of amorphous polyamide and aromatic polycarbonate, which layer provides adhesion between the polycarbonate and amorphous polyamide layer.
U.S. patent application Ser. No. 07/423309 filed Sep. 18, 1989, now abandoned and continuation patent application thereof Ser. No. 07/827,855 filed Jan. 30, 1992, both assigned to the same assignee of the instant patent application also discloses a multilayer container having an outer aromatic polycarbonate layer and an inner amorphous polyamide layer wherein the amorphous layer is composed of an amine functionalized polyamide. The multilayer container of the pending patent application Ser. No. 07/827,855 has good adhesion between the polycarbonate and the amine functionalized amorphous polyamide layer.
With the demand for containers that are reuseable in order to reduce the refuse problem facing the world, new concepts in thermoplastic resin bottles have been considered for such reuse to help solve the problem such as being rewashable and refillable. Certain polyethylene terephthalate (PET) bottles are not able to meet multiple rewashing and refilling. Heavy walled PET containers have been made but still lack the ability to withstand multiple wash cycles, particularly hot wash cycles because the PET containers are made of biaxially oriented PET. Thus when containers are rewashed at temperatures in excess of 60.degree. C. which is near the glass transition temperature (Tg) of the biaxially oriented PET, the container severely shrinks and thereby loses volume by shrinking down from its original capacity.
Other monolayer and certain multilayer containers started to emerge showing promise of having the ability to be rewashable and refillable. Success has been achieved for certain non-carbonated juices and non-carbonated water. Such containers are rewashable and refillable and some can even be hot filled with certain juices. However, successful containers for carbonated beverages wherein the containers have good gas barrier properties and can endure multiple rewashing and refilling are still wanted. With the large number of throw away plastic containers being disposed of daily, there is the need for multiple rewashable and refillable plastic containers for carbonated beverages.
Therefore, it is an object of the instant invention to provide a multilayer container that has the ability to withstand repeated washing cycles with hot solutions. Another object of the instant invention is to provide a multilayer container that is resistant to stress crazing and cracking when under internal pressure. Still another object of the instant invention is to provide a multilayer container that is rewashable and refillable for carbonated beverages while still maintaining clarity and container integrity.